In an optocoupler, a driver stage takes an input signal and converts it to an optical signal. The optical signal is then sensed by a detector stage which converts it back to an electrical signal. Ideally, the two stages (driver and detector) introduce little or no delay or distortion into the signal being coupled.
A detector stage offering high switching speed with minimal pulse width distortion and isolation would be highly desirable for an optocoupler. Such a detector can be fashioned with a detector responsive to changes in the output of a photo diode. A delay circuit retains the value of the detector output immediately preceding a change in the diode""s output to provide a dynamic reference level against which the instantaneous output of the detector is compared.